A dam is a hydraulic structure of fairly impervious material built across a river to create a reservoir on its upstream side for impounding water for various purposes. A detailed ppt on dams,its types,pros and cons.
Dams are massive barriers built across rivers and streams to confine
and utilize the flow of water for human purposes. These purposes may
be Irrigation, Hydropower, Water-supply, Flood Control, Navigation,
Fishing and Recreation. This confinement of water creates lakes or
REASONS TO BUILD A DAM
Dams have two main functions.
• The first is to store water to compensate for fluctuations in river flow or in
demand for water and energy.
• The second to raise the level of the water upstream to enable water to be
diverted into a canal or to increase ’hydraulic head’ –– the difference in
height between the surface of a reservoir and the river downstream.
• The creation of storage and head allow
• Dams to generate electricity (hydropower provides nearly a fifth of the world’s
• To supply water for agriculture, industries and households
• To control flooding
• To assist river navigation by providing regular flows and drowning rapids.
• Other reasons for building large dams include reservoir fisheries and
leisure activities such as boating.
• The earliest known dam is the
Jawa Dam in Jordan, 100
kilometres (62 mi) northeast of the
• This gravity dam featured an
originally 9-metre-high (30 ft) and
1 m-wide (3.3 ft) stone wall,
supported by a 50 m-wide (160 ft)
• The structure is dated to 3000 BC
Sadd-el-Kafara Dam, Egypt
Great Dam of Marib, Yemen
Kallanai Dam, India
2nd century AD
One of the oldest water-diversion or water-
regulator structures in the world which is still in use.
Dujiangyan irrigation system, China
The oldest surviving irrigation system
• Larger dam structures
• Large reservoir dams
• Pioneering use of water-proof
• Embankment dams
• Masonry gravity dams
• Arch-gravity dams
• Arch dams
• Buttress dams
• Multiple arch buttress dams
• First to build dam bridges
• Hydropower through water
• Water supply
Remains of the Band-e Kaisar dam, Iran,
built by the Romans in the 3rd century AD
The Roman dam at Cornalvo, Spain has
been in use for almost two millennia.
EARLY 19th CENTURY
Mir Alam dam, Hyderabad, India
Built in 1804 by Royal Engineers
Jones Falls Dam, Ontario Canada
When completed in 1832, the
Jones Falls dam was the largest dam
in North America
The 75-miles dam near
Built in 1880
World's first concrete arch
• The era of large dams was initiated with the construction of the Aswan Low
Dam in Egypt in 1902 by the British.
• When initially constructed between 1899 and 1902, nothing of its scale had
ever been attempted
• On completion, it was the largest masonry dam in the world.
• The Hoover Dam is a massive concrete arch-gravity dam
• Constructed in the black canyon of the Colorado river, on the border between
the US states of Arizona and Nevada between 1931 and 1936.
• Such a large concrete structure had never been built before, and some of the
techniques were unproven.
DIFFERENT PARTS & TERMINOLOGIES OF DAMS
• Crest: The top of the Dam. These may in some cases be used for
providing a roadway or walkway over the dam.
• Parapet walls: Low Protective walls on either side of the roadway or
walkway on the crest.
• Heel: Portion of Dam in contact with ground or river-bed at upstream
• Toe: Portion of dam in contact with ground or river-bed at
• Spillway: It is the arrangement made (kind of passage) near the top of
dam for the passage of surplus/excessive water from the reservoir.
• Abutments: The valley slopes on either side of the dam wall to which
the left & right end of dam are fixed to.
DIFFERENT PARTS & TERMINOLOGIES OF DAMS
• Gallery: Level or gently sloping tunnel like passage (small room like space)
at transverse or longitudinal within the dam with drain on floor for seepage
water. These are generally provided for having space for drilling grout holes
and drainage holes. These may also be used to accommodate the
instrumentation for studying the performance of dam.
• Sluice way: Opening in the dam near the base, provided to clear the silt
accumulation in the reservoir.
• Free board: The space between the highest level of water in the reservoir
and the top of the dam.
• Dead Storage level: Level of permanent storage below which the water will
not be withdrawn.
• Diversion Tunnel: Tunnel constructed to divert or change the direction of
water to bypass the dam construction site. The dam is built while the river
flows through the diversion tunnel
TYPES OF DAMS
• Arch dam
• Gravity dam
• Buttress dam
• Arch-gravity dam
• Embankment dam
• Rock-fill dam
• Concrete-face rock-fill dam
• Earth-fill dam
• Saddle dam
• Check dam
• Dry dam
• Diversionary dam
• Underground dam
• Tailings dam
• Steel dam
• Timber dam
• Natural dam
• Beaver dam
• An arch dam is a solid dam made of the bedrock
of the surrounding area that is curved upstream
• The arch dam is designed so that the force of the
water against it, known as hydrostatic pressure,
presses against the arch, compressing and
strengthening the structure as it pushes into its
foundation or abutments.
• An arch dam is most suitable for narrow gorges or
canyons with steep walls of stable rock to support
the structure and stresses.
• Since they are thinner than any other dam type,
they require much less construction material,
making them economical and practical in remote
• A gravity dam is a dam constructed from
concrete or stone masonry and designed
to hold back water by primarily utilizing
the weight of the material alone to resist
the horizontal pressure of water pushing
• Gravity dams are designed so that each
section of the dam is stable, independent
of any other dam section.
• Most gravity dams are straight.
• Some masonry and concrete gravity dams
have the dam axis curved to add stability
through arch action.
• A buttress dam or hollow dam is basically a
derivation of a gravity dam with the introduction
of intermediate space.
• With a buttress dam, the face of the dam is held
by a series of supports or buttresses that are
placed at intervals on the downstream side.
• The buttresses work to combat the force of
reservoir water from trying to push the dam over.
• The forces or laws of physics working against a
buttress dam are exactly the same as those that
act on a gravity dam except the vertical load
presented by the water on a buttress dam is
• The advantage of a buttress dam is that it typically
requires less concrete to construct than a gravity
• The formwork and reinforced steel used in the
building of buttresses is expensive, however, and
will ultimately offset any costs saved
• A gravity dam can be combined with
an arch dam into an arch-gravity dam
for areas with massive amounts of
water flow but less material available
for a purely gravity dam.
• The inward compression of the dam by
the water reduces the lateral
(horizontal) force acting on the dam.
• Thus, the gravitation force required by
the dam is lessened, i.e. the dam does
not need to be so massive.
• This enables thinner dams and saves
resources. Hoover Dam, USA
• A special kind of dam which
consists of a line of large gates
that can be opened or closed to
control the amount of water
passing the dam.
• The gates are set between
flanking piers which are
responsible for supporting the
water load, and are often used
to control and stabilize water
flow for irrigation systems
• They are massive dams made of earth
• Like gravity dams, embankment dams
rely on their heavy weight to resist
the force of the water.
• But embankment dams are also
armed with a dense, waterproof core
that prevents water from seeping
through the structure.
• Embankment dams are of two main
types, rock-fill and earth-fill dams.
EARTHFILL DAM & ROCK-FILL DAM
• Rock-fill dams are embankments of
compacted free-draining granular earth with
an impervious zone.
• The earth utilized often contains a high
percentage of large particles, hence the term
• The impervious zone may be on the
upstream face and made of masonry,
concrete, plastic membrane, steel sheet
piles, timber or other material.
• Earthfill dam, also called Earth Dam, or
• Dam built up by compacting successive layers of
earth, using the most impervious materials to form
a core and placing more permeable substances on
the upstream and downstream sides.
• A facing of crushed stone prevents erosion by wind
or rain, and an ample spillway, usually of concrete,
protects against catastrophic washout should the
water overtop the dam.
Concrete-face Rock-fill Dam (CFRD)
• A concrete-face rock-fill dam (CFRD)
is a rock-fill dam with concrete
slabs on its upstream face.
• This design provides the concrete
slab as an impervious wall to
prevent leakage and also a
structure without concern for uplift
• In addition, the CFRD design is
flexible for topography, faster to
construct and less costly than
Mohale Dam, Lesotho
SADDLE DAM & WEIR
Saddle dam is a subsidiary dam of any type
constructed across a saddle or low point on
the perimeter of a reservoir.
A weir (overflow dam) is a type of small
overflow dam that is often used within a
river channel to create an impoundment
lake for water abstraction purposes and
which can also be used for flow
measurement or retardation.
CHECK DAM & DRY DAM
• A check dam is a small dam designed to
reduce flow velocity and control soil
• A dry dam, also known as a flood
retarding structure, is a dam designed to
• It normally holds back no water and
allows the channel to flow freely, except
during periods of intense flow that would
otherwise cause flooding downstream.
DIVERSIONARY DAM & UNDERGROUND DAM
A diversionary dam is a structure designed to
divert all or a portion of the flow of a river from
its natural course. The water may be redirected
into a canal or tunnel for irrigation and/or
hydroelectric power production.
• Underground dams are used to trap
groundwater and store all or most of it below
the surface for extended use in a localized
• In some cases they are also built to prevent
saltwater from intruding into a freshwater
• Underground dams are typically constructed
in areas where water resources are minimal
and need to be efficiently stored, such as in
deserts and on islands
• A tailings dam is typically an earth-fill embankment dam used to store by-
products, which are produced during mining operations after separating
the valuable fraction from the uneconomic fraction of an ore.
STEEL DAM & TIMBER DAM
• A steel dam is a type of dam briefly
experimented with around the start of the
20th century which uses steel plating (at an
angle) and load-bearing beams as the
• The steel dams were an (arguably failed)
• Timber dams were widely used in the early
part of the industrial revolution and in
frontier areas due to ease and speed of
• Rarely built in modern times because of their
relatively short lifespan and the limited height
to which they can be built, timber dams must
be kept constantly wet in order to maintain
their water retention properties and limit
deterioration by rot, similar to a barrel.
COFFERDAM & NATURAL DAM
• A cofferdam (also called a coffer) is a
temporary enclosure built within, or in
pairs across, a body of water and
constructed to allow the enclosed area to
be pumped out.
• Such structures are typically dismantled
after the ultimate work is completed.
• Dams can also be created by natural geological
• Natural disasters such as earthquakes and
landslides frequently create landslide dams in
• Natural dams often pose significant hazards to
human settlements and infrastructure.
• Beavers create dams primarily out of mud and sticks to flood a particular
• By flooding a parcel of land, beavers can navigate below or near the surface and
remain relatively well hidden or protected from predators.
• The flooded region also allows beavers access to food, especially during the
POWER GENERATION PLANT
• Hydropower is the leading renewable source for electricity generation
globally, supplying 71% of all renewable electricity at the end of 2015.
• Undeveloped potential is approximately 10 000 TWh/y worldwide.
• The global hydropower capacity increased by more than 30% between 2007 and
2015 accounting to a total of 1209 GW in 2015, of which 145 GW is pumped
Hydroelectric dam in cross section
Hydraulic turbine and electric generator
• A spillway is a section of a dam designed to pass water from the
upstream side of a dam to the downstream side.
• Many spillways have floodgates designed to control the flow through
THREE GORGES DAM, CHINA
The Three Gorges Dam, the hydroelectric dam is the world's largest power
station by installed capacity (22,500 MW)
ITAIPU DAM (BRAZIL-PARAGUAY)
Itaipu is the hydroelectric plant that produces more energy in the world, setting a
new world 103,098,366 megawatt hour (MWh) record in 2016 and had surpassed the
Three Gorges Dam plant in 2016 and 2015 in energy production.
FACTORS AFFECTING SELECTION OF TYPE OF DAM
• Geology and Foundation Conditions
• Availability of materials
• Spillway size and location
• Earthquake zone
• Height of the Dam
• Other factors such as cost of construction and maintenance, life of
dam, aesthetics etc.
SELECTION OF DAM SITE
• Suitable foundation must be available.
• For economy, the length of the dam should be as small as possible, and for a
given height, it should store the maximum volume of water.
• The general bed level at dam site should preferably be higher than that of the
river basin. This will reduce the height of the dam.
• A suitable site for the spillway should be available in the near vicinity.
• Materials required for the construction of dam should be easily available, either
locally or in the near vicinity.
• The value of land and property submerged by the proposed dam should be as low
• The dam site should be easily accessible, so that it can be economically
connected to important towns and cities.
• Site for establishing labor colonies and a healthy environment should be available
near the site.
ADVANTAGES OF DAMS
• Clean, efficient, and reliable form of energy.
• Does not emit any direct pollutants or greenhouse gases.
• While the initial cost is high, they are very inexpensive to operate.
• Electricity generated by hydro-electric power plants is the cheapest
• Dams prevent floods.
• Dams store water for irrigation in summer seasons and dry months.
Many desert areas can now farm due to dams and canals that supply
• Dams supply water for local drinking needs.
• Allows for fish farming.
NEGATIVE IMPACT OF DAMS
• In flat basins large dams cause flooding of large tracts of land, destroying local animals and habitats.
• People have to be displaced causing change in life style and customs, even causing emotional
scarring. About 40 to 80 million people have been displaced physically by dams worldwide.
• Large amounts of plant life are submerged and decay anaerobically (in the absence of oxygen)
generating greenhouse gases like methane. It is estimated that a hydroelectric power plant
produces 3.5 times the amount of greenhouse gases as a thermal power plant burning fossil fuels.
• The migratory pattern of river animals like salmon and trout are affected.
• Dams restrict sediments that are responsible for the fertile lands downstream. Farmers use
chemical fertilizers and pesticides to compensate for the loss in productivity.
• Salt water intrusion into the deltas means that the saline water cannot be used for irrigation.
• Large dams are breeding grounds for mosquitoes and cause the spread of disease.
• Farmers downstream who used to wait for the flooding of the fields to plant their seeds are
• Dams serve as a heat sink, and the water is hotter than the normal river water. This warm water
when released into the river downstream can affect animal life.
• Peak power operations can change the water level thirty to forty feet in one day and can kill the
animals staying at the shorelines.
• Around 400,000 km2 of land worldwide has been submerged due to the construction of dams.
SOLUTION TO THE PROBLEMS
Negative effects on flora, fauna, and the local population can be reduced by
the following methods:
• Fish passages should be created to aid in the migration of the fish.
• New dam sites should be chosen with the environmental impacts in mind.
• Local people should be led into confidence and must be suitably re-settled.
• Proper compensation as per the market rate should be given.
• Religious monuments of historic significance should be shifted.
• Endangered species can be relocated.
If the political will to change and do a good job is there a dam can be
constructed in a way to minimize its effects on people and the environment.
Dams have made an important and significant contribution to human
development, and the benefits derived from them have been
considerable. Dam building has been one of the most disputed topics
affecting the environment today. The push and pull between the pros
and cons have created conflicts among different groups. While dams
destroy the nature and people surrounding the area in which they are
built, they do provide people with water and products from water. The
solutions are minimal, but the damages could be decreased depending
on the placement of the dam.
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